The invention relates to agricultural combines and systems for controlling their operation. More particularly, it relates to control systems for obtaining the hydraulic system pressure of a rotor drive when dedicated transducers are not available.
Hydro-mechanical drive systems for combine rotors monitor a variety of system parameters when controlling the engagement, disengagement and speed of combine rotors. They typically have a variety of sensors that sense physical system parameters pressures, speeds, temperatures and positions of the various components comprising the systems.
Normally, physical system parameters, which are necessary for the feedback control algorithms and the display of data to the operator, are measured directly by using sensors. For example, a pressure sensor coupled to a hydraulic fluid conduit may directly indicate the hydraulic system pressure of the drive system. Other sensors may directly measure such parameters as rotor speed, shaft speed, oil temperature and the like.
Each sensor adds cost to the vehicle. Furthermore, it may be difficult if not impossible to measure certain parameters because of inaccessibility, sensor unreliability or the like. Because of these limitations it would be beneficial to eliminate one or more sensors to reduce the cost, reduce the size, and increase the reliability of the combine and its control systems.
One system parameter that may be estimated rather than sensed directly is hydraulic system pressure. Hydraulic system pressure is one of the indices used to determine if a rotor is staring to become slugged. The pressure can be sensed directly by a hydraulic fluid pressure sensor. Alternatively, and as disclosed in the present application, it can be estimated using a variety of other measured system parameters.
Once estimated, it can be used in a traditional control process such as delivering a warning to the operator that rotor slugging, engine stalling, or other mechanical damage is imminent.
Hydraulic system pressure is a particularly useful measure of rotor slugging (i.e. rotor jamming or plugging) in a combine that employs a PID feedback control loop to maintain the rotor speed constant, such as in the present system. In combines having such a control system, increasing loads on the motor experienced when the rotor begins to slug or jam, are not indicated by another parameter such as motor or rotor speed.
When a PID control algorithm is used to keep the rotor operating at a constant speed, increased load on the rotor results in increased hydraulic fluid pressure to the hydraulic motor driving the rotor. This increased pressure produces more torque to keep the rotor operating at its constant selected speed. In short, as the load increases, the system compensates by applying increased hydraulic pressure to the motor to maintain the motor (and hence the rotor it drives) at a constant speed. It is hydraulic system pressure, not motor or rotor speed, that more accurately indicates incipient slugging of the rotor.
It is an object of this invention to provide a system that will estimate hydraulic system pressure without using a separate hydraulic system pressure sensor.
It is a further object of this invention to provide a system that will predict rotor slugging and to indicate incipient slugging to the operator,
In accordance with a first aspect of the invention an agricultural combine is provided, including a chassis; an internal combustion engine mounted on the chassis; a drive system coupled to the engine, the drive system including: a hydraulic pump coupled to the engine to be driven thereby to provide hydraulic fluid under pressure; a hydraulic motor in fluid communication with the hydraulic pump to receive the hydraulic fluid under pressure and be driven thereby; a multi-speed gearbox having a plurality of selectable gear ratios; a rotor driven by the gearbox and configured to thresh agricultural products; and an electronic control system including: an engine speed sensor coupled to the engine to generate a signal indicative of engine speed; a motor speed sensor coupled to the motor to generate a signal indicative of motor speed; and at least one electronic controller coupled to the motor speed sensor and the engine speed sensor and the pump displacement signal and configured to estimate the pressure of the hydraulic fluid under pressure.
In accordance with a second aspect of the invention, a control system for estimating a hydraulic pressure in a work vehicle, is provided, the work vehicle having at least a hydraulic pump and a hydraulic motor coupled together by hydraulic conduits, the conduits being configured to bi-directionally transit hydraulic fluid between the pump and the motor, the control system comprising: a motor speed sensor coupled to the motor to generate a signal indicative of the motor speed; a pump speed sensor coupled to the pump to generate a signal indicative of the pump speed; and at least one electronic controller including a digital microprocessor and an electronic digital memory coupled to the motor speed sensor and the pump speed sensor, the electronic controller being configured to receive a signal indicative of the motor speed, and a signal indicative of the pump speed, and a signal indicative of pump displacement, and to estimate a hydraulic fluid pressure in the conduits based upon the motor speed signal, the pump displacement, and the pump speed signal.